1. Field of the Invention
The present invention relates to the maintenance of high-voltage electrical equipment, and particularly to a system and method for contamination monitoring of high voltage insulators that provides for transmission of an alarm signal when contaminant levels (such as equivalent salt deposit density (ESDD) levels) formed on a high voltage insulator exceed pre-selected threshold values, indicating the likelihood of high voltage insulator failure.
2. Description of the Related Art
FIG. 2 illustrates a typical high voltage insulator I. Conventional high voltage transmission lines L typically use modular cap and pin insulators, such as high voltage insulator I. The wires or lines L are suspended from a string of substantially identical disc-shaped insulators D that are attached to each other with metal clevis pin or ball-and-socket links. The advantage of this design is that insulator strings with different breakdown voltages, for use with different line voltages, can be constructed by using different numbers of the basic units (i.e., different numbers of disc-shaped insulators D). The breakdown voltage of an insulator is the minimum voltage that causes a portion of the insulator to become electrically conductive.
When an insulator is polluted or wet, its ability to withstand mechanical and electrical stresses, as well as its flashover voltage, is greatly reduced. Contaminant particles in the presence of moisture form conducting films on the surfaces of discs D, allowing leakage currents to form and be transmitted. This current heats the surfaces, leading to formation of dry bands in areas of high current density. High voltages then build up across those bands, which may cause partial discharges, leading to insulator flashover.
Insulator surface contamination, and subsequent flow of leakage current, has caused operating problems for electric power utilities since electrical power has been in use. The effect of leakage current and insulator flashover is a major practical concern for continuity of electric power supply.
Detection of a failed or contaminated insulator requires either visual inspection or disruption of the normal electrical power supply. In other words, failure must first occur before repairs can be made. It would be desirable to provide an early predictor for high voltage insulator failure, allowing repairmen to either already be on site when the insulator fails, in order to expedite repair time, or to allow repair and/or replacement of a faulty insulator before the failure actually occurs.
Insulator contamination is often a result of exposure to various pollution types, including desert sandstorms, airborne salt from the sea, industrial pollution, high humidity and fog, in addition to high ambient temperatures and large ambient temperature differences within a 24-hour cycle. Typically, electric utilities perform scheduled periodic high-pressure water, live-line and sub-station insulator washing. The practice of periodic insulator washing is not particularly cost effective, due to the fact that insulator performance is determined by a number of parameters, some of which are variable and mostly unpredictable.
Thus, a system and method for contamination monitoring of high voltage insulators solving the aforementioned problems is desired.